Defining the carbohydrate specificities of Abrus precatorius agglutinin as T (Gal beta 1—-3GalNAc) greater than I/II (Gal beta 1—-3/4GlcNAc)

Recent advances in the use of legume lectins for the diagnosis and treatment of breast cancer

Poor lifestyle choices and genetic predisposition are factors that increase the number of cancer cases, one example being breast cancer, the third most diagnosed type of malignancy. Currently, there is a demand for the development of new strategies to ensure early detection and treatment options that could contribute to the complete remission of breast tumors, which could lead to increased overall survival rates. In this context, the glycans observed at the surface of cancer cells are presented as efficient tumor cell markers. These carbohydrate structures can be recognized by lectins which can act as decoders of the glycocode. The application of plant lectins as tools for diagnosis/treatment of breast cancer encompasses the detection and sorting of glycans found in healthy and malignant cells. Here, we present an overview of the most recent studies in this field, demonstrating the potential of lectins as: mapping agents to detect differentially expressed glycans in breast cancer, as histochemistry/cytochemistry analysis agents, in lectin arrays, immobilized in chromatographic matrices, in drug delivery, and as biosensing agents. In addition, we describe lectins that present antiproliferative effects by themselves and/or in conjunction with other drugs in a synergistic effect.

Increasing the depth of mass spectrometry-based glycomic coverage by additional dimensions of sulfoglycomics and target analysis of permethylated glycans

Hog or porcine gastric mucin resembles the human source in carrying not only blood group antigens but also the rather rare α4-GlcNAc-capped terminal epitope functionally implicated in protection against Helicobacter pylori infection. Being more readily available and reasonably well characterized, it serves as a good reagent for immunobiological studies, as well as a standard for analytical methodology developments. Current approaches in mass spectrometry (MS)-based glycomic mapping remain vastly inadequate in revealing the full complexity of glycosylation, particularly for cases such as the extremely heterogeneous O-glycosylation of mucosal mucins that can be further sulfated. We demonstrate here a novel concerted workflow that extends the conventional matrix-assisted laser desorption/ionization–mass spectrometry (MALDI-MS) mapping of permethylated glycans in positive ion mode to include a further step of sulfoglycomic analysis in negative ion mode. This was facilitated by introducing a mixed-mode solid-phase extraction step, which allows direct cleanup and simultaneous fractionation of the permethylated glycans into separate non-sulfated and sulfated pools in one single step. By distinct MALDI-MS/MS fragmentation patterns, all previously known structural features of porcine gastric mucin including the terminal epitopes and location of sulfates could be readily defined. We additionally showed that both arms of the core 2 structures could be extended via 6-O-sulfated GlcNAc to yield a series of disulfated O-glycans not previously reported, thus expanding its current glycomic coverage. However, a targeted LC-MSn analysis was required and best suited to dig even deeper into validating the occurrence of very minor structural isomers carrying the Lewis Y epitope implicated by positive antibody binding.

Lectins as tools in glycoconjugate research

Lectins are ubiquitous proteins of nonimmune origin, present in plants, microorganisms, animals and humans which specifically bind defined monosugars or oligosaccharide structures. Great progress has been made in recent years in understanding crucial roles played by lectins in many biological processes. Elucidation of carbohydrate specificity of human and animal lectins is of great importance for better understanding of these processes. Long before the role of carbohydrate-protein interactions had been explored, many lectins, mostly of plant origin, were identified, characterized and applied as useful tools in studying glycoconjugates. This review focuses on the specificity-based lectin classification and the methods of measuring lectin-carbohydrate interactions, which are used for determination of lectin specificity or for identification and characterization of glycoconjugates with lectins of known specificity. The most frequently used quantitative methods are shortly reviewed and the methods elaborated and used in our laboratories, based on biotinylated lectins, are described. These include the microtiter plate enzyme-linked lectinosorbent assay, lectinoblotting and lectin-glycosphingolipid interaction on thin-layer plates. Some chemical modifications of lectin ligands on the microtiter plates and blots (desialylation, Smith degradation, beta-elimination), which extend the applicability of these methods, are also described.

Expression of sialyl Lex, sialyl Lea, Lex and Ley glycotopes in secreted human ovarian cyst glycoproteins

Human blood group A, B, H, Ii, Le(a) and Le(b) antigens and their determinants expressed on ovarian cyst glycoproteins have been studied for over five decades. However, little is known about sialyl Le(x) and sialyl Le(a) glycotopes, which play essential roles in normal immunity, inflammation, and cancer cell metastasis. Furthermore, Le(x) and Le(y) were classified as glycotopes of unknown genes. Identification of these Lewis epitopes was hampered by the lack of specific antibodies. In this study, the occurrence of sialyl Le(x), sialyl Le(a), Le(x) and Le(y) reactivities in cyst glycoproteins was characterized by enzyme-linked immunosorbent assays. The results indicated that most human ovarian cyst glycoproteins carried Le(x) (8/25) and/or Le(y) (17/25) glycotopes. The expression (epitopes) of the new genes described in previous reports are Le(x) and Le(y) glycotopes; the reactivities of sialyl Le(x) and sialyl Le(a) glycotopes in secreted cyst glycoproteins may be affected by the conditions of purification; the relationship between Le(y) and human blood group ABH was confirmed; recognition profiles of sialyl Le(x), sialyl Le(a), Le(x) and Le(y) present in the carbohydrate chains of water-soluble cyst glycoproteins were illustrated; possible attachments of glycotopes to the internal carbohydrate complex of cyst glycoproteins have been reconstructed; proposed biosynthetic pathways for the formation of sialyl Le(a), sialyl Le(x), Le(x), Le(y), ALe(y) and BLe(y) determinant structures on Type I and Type II core structures of human ovarian cyst glycoproteins are also included in this study.

Differential contributions of recognition factors of two plant lectins -Amaranthus caudatus lectin and Arachis hypogea agglutinin, reacting with Thomsen-Friedenreich disaccharide (Galbeta1-3GalNAcalpha1-Ser/Thr)

Previous reports on the carbohydrate specificities of Amaranthus caudatus lectin (ACL) and peanut agglutinin (PNA, Arachis hypogea) indicated that they share the same specificity for the Thomsen-Friedenreich (T(alpha), Galbeta1-3GalNAcalpha1-Ser/Thr) glycotope, but differ in monosaccharide binding--GalNAc>>Gal (inactive) for ACL; Gal>>GalNAc (weak) with respect to PNA. However, knowledge of the recognition factors of these lectins was based on studies with a small number monosaccharides and T-related oligosaccharides. In this study, a wider range of interacting factors of ACL and PNA toward known mammalian structural units, natural polyvalent glycotopes and glycans were examined by enzyme-linked lectinosorbent and inhibition assays. The results indicate that the main recognition factors of ACL, GalNAc was the only monosaccharide recognized by ACL as such, its polyvalent forms (poly GalNAcalpha1-Ser/Thr, Tn in asialo OSM) were not recognized much better. Human blood group precursor disaccharides Galbeta1-3/4GlcNAcbeta (I(beta)/II(beta)) were weak ligands, while their clusters (multiantennary II(beta)) and polyvalent forms were active. The major recognition factors of PNA were a combination of alpha or beta anomers of T disaccharide and their polyvalent complexes. Although I(beta)/II(beta) were weak haptens, their polyvalent forms played a significant role in binding. From the 50% molar inhibition profile, the shape of the ACL combining site appears to be a cavity type and most complementary to a disaccharide of Galbeta1-3GalNAc (T), while the PNA binding domain is proposed to be Galbeta1-3GalNAcalpha or beta1--as the major combining site with an adjoining subsite (partial cavity type) for a disaccharide, and most complementary to the linear tetrasaccharide, Galbeta1-3GalNAcbeta1-4Galbeta1-4Glc (T(beta)1-4L, asialo GM(1) sequence). These results should help us understand the differential contributions of polyvalent ligands, glycotopes and subtopes for the interaction with these lectins to binding, and make them useful tools to study glycosciences, glycomarkers and their biological functions.

Differential affinities of Erythrina cristagalli lectin (ECL) toward monosaccharides and polyvalent mammalian structural units

Previous studies on the carbohydrate specificities of Erythrina cristagalli lectin (ECL) were mainly limited to analyzing the binding of oligo-antennary Galbeta1-->4GlcNAc (II). In this report, a wider range of recognition factors of ECL toward known mammalian ligands and glycans were examined by enzyme-linked lectinosorbent and inhibition assays, using natural polyvalent glycotopes, and a glycan array assay. From the results, it is shown that GalNAc was an active ligand, but its polyvalent structural units, in contrast to those of Gal, were poor inhibitors. Among soluble natural glycans tested for 50% molecular mass inhibition, Streptococcus pneumoniae type 14 capsular polysaccharide of polyvalent II was the most potent inhibitor; it was 2.1 x 10(4), 3.9 x 10(3) and 2.4 x 10(3) more active than Gal, tri-antennary II and monomeric II, respectively. Most type II-containing glycoproteins were also potent inhibitors, indicating that special polyvalent II and Galbeta1-related structures play critically important roles in lectin binding. Mapping all information available, it can be concluded that: [a] Galbeta1-->4GlcNAc (II) and some Galbeta1-related oligosaccharides, rather than GalNAc-related oligosaccharides, are the core structures for lectin binding; [b] their polyvalent II forms within macromolecules are a potent recognition force for ECL, while II monomer and oligo-antennary II forms play only a limited role in binding; [c] the shape of the lectin binding domains may correspond to a cavity type with Galbeta1-->4GlcNAc as the core binding site with additional one to four sugars subsites, and is most complementary to a linear trisaccharide, Galbeta1-->4GlcNAcbeta1-->6Gal. These analyses should facilitate the understanding of the binding function of ECL.

Interactions of the fucose-specific Pseudomonas aeruginosa lectin, PA-IIL, with mammalian glycoconjugates bearing polyvalent Lewisa and ABH blood group glycotopes

Pseudomonas aeruginosa Fuc > Man specific lectin, PA-IIL, is an important microbial agglutinin that might be involved in P. aeruginosa infections in humans. In order to delineate the structures of these lectin receptors, its detailed carbohydrate recognition profile was studied both by microtiter plate biotin/avidin-mediated enzyme-lectin-glycan binding assay (ELLSA) and by inhibition of the lectin-glycan interaction. Among 40 glycans tested for binding, PA-IIL reacted well with all human blood group ABH and Le(a)/Le(b) active glycoproteins (gps), but weakly or not at all with their precursor gps and N-linked gps. Among the sugar ligands tested by the inhibition assay, the Le(a) pentasaccharide lacto-N-fucopentaose II (LNFP II, Galbeta1-3[Fucalpha1-4]GlcNAcbeta1-3Galbeta1-4Glc) was the most potent one, being 10 and 38 times more active than the Le(x) pentasaccharide (LNFP III, Galbeta1-4 [Fucalpha1-3]GlcNAcbeta1-3Galbeta1-4Glc) and sialyl Le(x) (Neu5Acalpha2-3Galbeta1-4[Fucalpha1-3] GlcNAc), respectively. It was 120 times more active than Man, while Gal and GalNAc were inactive. The decreasing order of PA-IIL affinity for the oligosaccharides tested was: Le(a) pentaose > or = sialyl Le(a) tetraose > methyl alphaFuc > Fuc and Fucalpha1-2Gal (H disaccharide)>2'-fucosyllactose (H trisaccharide), Le(x) pentaose, Le(b) hexaose (LNDFH I) and gluco-analogue of Le(y) tetraose (LDFT)>H type I determinant (LNFP I)>Le(x) trisaccharide (Galbeta1-4[Fucalpha1-3]GlcNAc) > sialyl Le(x) trisaccharide >> Man >>> Gal, GalNAc, and Glc (inactive). The results presented here, in accordance with the crystal 3D structural data, imply that the combining site of PA-IIL is a small cavity-type best fitting Fucalpha1- with a specific shallow groove subsite for the remainder part of the Le(a) saccharides, and that polyvalent glycotopes enhance the reactivity. The Fuc > Man Ralstonia solanacearum lectin RSL, which resembles PA-IIL in sugar specificity, differs from it in it's better fit to the B and A followed by H oligosaccharides vs. Fuc, whereas, the second R. solanacearum lectin RS-IIL (the structural homologue of PA-IIL) binds Man > Fuc. These results provide a valuable information on PA-IIL interactions with mammalian glycoforms and the possible spectrum of attachment sites for the homing of this aggressive bacterium onto the target molecules. Such information might be useful for the antiadhesive therapy of P. aeruginosa infections.

Recognition profile of Morus nigra agglutinin (Morniga G) expressed by monomeric ligands, simple clusters and mammalian polyvalent glycotopes

The carbohydrate binding properties of a novel member of the subfamily of galactose-specific jacalin-related lectin isolated from the bark of black mulberry (Morus nigra) (Morniga G) was studied in detail by enzyme-linked lectinosorbent and inhibition assays using panels of monomeric saccharides, mammalian polyvalent glycotopes and polysaccharides. Among the natural glycans tested for lectin binding, Morniga G reacted best with glycoproteins (gps) presenting a high density of tumor-associated carbohydrate antigens Tn (GalNAcalpha1-Ser/Thr) and Talpha (Galbeta1-3GalNAcalpha1-). Their reactivities, on a nanogram basis, were up to 72.5, 3.9x10(3), 6.0x10(3), 8.8x10(3) and 2.9x10(4) times higher than that of Tn-containing glycopeptides (M.W.<3000 Da), monomeric T, Tn, GalNAc and Gal, respectively. It also reacted well with many multi-antennary N-glycans with II (Galbeta1-4GlcNAc) termini, ABH histo-blood group antigens and their precursors containing high densities of I/II and T/Tn glycotopes, and sialylated T/Tn. Among the mono-, di- and oligosaccharides tested, Thomsen-Friedenreich (T) disaccharide with aromatic aglycon [Galbeta1-3GalNAcalpha1-benzyl (Talpha1-benzyl)] and Tn glycopeptides were the best inhibitors. Molecular modeling and docking studies indicated the occurrence of a primary GalNAcalpha1- and Galbeta1-3GalNAc glycotope-binding site in Morniga G. Using a recently proposed system [Wu, A.M., 2003. Carbohydrate structural units in glycoproteins and polysaccharides as important ligands for Gal and GalNAc reactive lectins. J. Biomed. Sci. 10, 676-688], the binding properties of the combining sites of Morniga G can be defined as follows: (i) the monosaccharide specificity is GalNAc/Gal>>Man/Glc, GlcNAc and lFuc; (ii) the mammalian glycotope specificity is Talpha1-benzyl>T>Tn>GalNAcbeta1-3Gal (P), while B/E (Galalpha1-3/4Gal), I/II (Galbeta1-3/4GlcNAc), S (GalNAcbeta1-4Gal), F/A (GalNAcalpha1-3GalNAc/Gal) and L (Galbeta1-4Glc) are inactive; (iii) the most active ligand is T/Tn; (iv) simple clustered Tn or triantennary N-glycans with II termini (Tri-II) have limited impact; (v) high-density polyvalent glycotopes play a prominent role for enhancing Morniga G reactivity. These results provide evidence for the binding of this lectin to dense cell surface T/Tn glycoconjugates and facilitate future usage of this lectin in biotechnological and medical applications.

Recognition factors of Ricinus communis agglutinin 1 (RCA1)

Ricinus communis agglutinin (RCA1) is one of the most important applied lectins that has been widely used as a tool to study cell surfaces and to purify glycans. Although the carbohydrate specificity of RCA1 has been described, the information obtained was mainly focused on inhibition of simple Galbeta1-related oligosaccharides and simple clusters. Here, all possible recognition factors of RCA1 of glycan binding were examined by enzyme-linked lectinosorbent (ELLSA) and inhibition assays, using known mammalian Gal/GalNAc carbohydrate structural units and natural polyvalent glycans. Among the glycoproteins (gps) tested and expressed as 50% nanogram inhibition, the high-density polyvalent Galbeta1-4GlcNAc (II) glycotopes occurring in natural gps, such as Pneumococcus type 14 capsular polysaccharide which is composed of repeating poly II residues, resulted in 9.0 x 10(4), 1.5 x 10(5), 2.3 x 10(4) and 2.1 x 10(4)-fold higher affinities to RCA1 than the monomeric Gal, linear I/II and Tri-antennary-II (Tri-II). Of the ligands tested and expressed as nanomoles of 50% inhibition, Tri-II was the best, being about 2, 4, 25.6 and 33.3 times better inhibitor than Di-II, II, I (Galbeta1-3GlcNAc) and Gal, respectively. From the results of this study, it is concluded that: (a) Galbeta1-4GlcNAc and other Galbeta1-related oligosaccharides are essential for lectin binding and their polyvalent form in macromolecules should be the most important recognition factor for RCA1; (b) the combining site of RCA1 may be a groove type, recognizing Galbeta1-4GlcNAc (II) as the major binding site; (c) its combining size may be large enough to accommodate a tetrasaccharide of beta-anomeric Gal at the non-reducing end and most complementary to human blood group I Ma active trisaccharide (Galbeta1-4GlcNAcbeta1-6Gal) and lacto-N-neotetraose (Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc); (d) RCA1 has a preference for the beta-anomer of Gal oligosaccharides with a Galbeta1-4 linkage > Galbeta1-6 > or = Galbeta1-3; (e) configuration of carbon-2, -3 -4 and -6 in Gal are essential for binding; (f) hydrophobic interaction in the vicinity of the binding site useful for sugar accommodation increases affinity. These results should be helpful for understanding the functional role of RCA1 and for characterizing glycotopes of mammalian complex carbohydrates.

Carbohydrate recognition factors of the lectin domains present in the Ricinus communis toxic protein (ricin)

Ricin (RCA60) is a potent cytotoxic protein with lectin domains, contained in the seeds of the castor bean Ricinus communis. It is a potential biohazard. To corroborate the biological properties of ricin, it is essential to understand the recognition factors involved in the ricin-glycotope interaction. In previous reports, knowledge of the binding properties of ricin was limited to oligosugars and glycopeptides with different specificities. Here, recognition factors of the lectin domains in ricin were examined by enzyme-linked lectinosorbent (ELLSA) and inhibition assays, using mammalian Gal/GalNAc structural units and corresponding polyvalent forms. Except for blood group GalNAcalpha1-3Gal (A) active and Forssman (GalNAcalpha1-3GalNAc, F) disaccharides, ricin has a broad range of affinity for mammalian disaccharide structural units-Galbeta1-4Glcbeta1-(Lbeta), Galbeta1-4GlcNAc (II), Galbeta1-3GlcNAc (I), Galbeta1-3GalNAcalpha1-(Talpha), Galbeta1-3GalNAcbeta1-(Tbeta), Galalpha1-3Gal (B), Galalpha1-4Gal (E), GalNAcbeta1-3Gal (P), GalNAcalpha1-Ser/Thr (Tn) and GalNAcbeta1-4Gal (S). Among the polyvalent glycotopes tested, ricin reacted best with type II-containing glycoproteins (gps). It also reacted well with several T (Thomsen-Friedenreich), tumor-associated Tn and blood group Sd. (a+)-containing gps. Except for bird nest and Tamm-Horsfall gps (THGP), this lectin reacted weakly or not at all with ABH-blood type and sialylated gps. From the present and previous results, it can be concluded that: (i) the combining sites of these lectin domains should be a shallow-groove type, recognizing Galbeta1-4Glcbeta1- and Galbeta1-3(4)GlcNAcbeta- as the major binding site; (ii) its size may be as large as a tetrasaccharide and most complementary to lacto-N-tetraose (Galbeta1-3GlcNAc beta1-3Galbeta1-4Glc) and lacto-N-neotetraose (Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc); (iii) the polyvalency of glycotopes, in general, enhances binding; (iv) a hydrophobic interaction in the vicinity of the binding site for sugar accommodation, increases the affinity for Galbeta-. This study should assist in understanding the glyco-recognition factors involved in carbohydrate-toxin interactions in biological processes. The effect of the polyvalent P/S glycotopes on ricin binding should be examined. However, this is hampered by the lack of availability of suitable reagents.

Polyvalent GalNAcalpha1-->Ser/Thr (Tn) and Galbeta1-->3GalNAcalpha1-->Ser/Thr (T alpha) as the most potent recognition factors involved in Maclura pomifera agglutinin-glycan interactions

The agglutinin isolated from the seeds of Maclura pomifera (MPA) recognizes a mucin-type disaccharide sequence, Galbeta1-->3GalNAc (T) on a human erythrocyte membrane. We have utilized the enzyme-linked lectinosorbent assay (ELLSA) and inhibition assay to more systematically analyze the carbohydrate specificity of MPA with glyco-recognition factors and mammalian Gal/GalNAc structural units in lectin-glycoform interactions. From the results, it is concluded that the high densities of polyvalent GalNAcalpha1-->Ser/Thr (Tn) and Galbeta1-->3GalNAcalpha1-->Ser/Thr (T(alpha)) glycotopes in macromolecules are the most critical factors for MPA binding, being on a nanogram basis 2.0 x 10(5), 4.6 x 10(4) and 3.9 x 10(4) more active than monovalent Gal, monomeric T and Tn glycotope, respectively. Other carbohydrate structural units in mammalian glycoconjugates, such as human blood group Sd (a+) related disaccharide (GalNAcbeta1-->4Gal) and Pk/P1 active disaccharide (Galalpha1-->4Gal) were inactive. These results demonstrate that the configurations of carbon-4 and carbon-2 are essential for MPA binding and establish the importance of affinity enhancement by high-density polyvalencies of Tn/T glycotopes in MPA-glycan interactions. The overall binding profile of MPA can be defined in decreasing order as high density of polyvalent Tn/T(alpha) (M.W. > 4.0 x 10(4)) >> Tn-containing glycopeptides (M.W. < 3.0 x 10(3)) > monomeric T/Tn and P (GalNAcbeta1-->3Gal) > GalNAc > Gal >> Man, L: ARA: , D: Fuc and Glc (inactive). Our findings should aid in the selection of this lectin for elucidating functions of carbohydrate chains in life processes and for applications in the biomedical sciences.

Embryotoxic activity and differential binding of plant-derived carbohydrate-recognizing proteins towards the sea urchin embryo cells

The embryotoxic activity and differential binding of plant-derived carbohydrate-recognizing proteins on sea urchin (Lytechinus variegatus) embryo cells was investigated. IC50 doses for toxicity on larvae development varied from 0.6 up to 96.3 microg ml(-1) and these effects were largely reversed by previously heating the proteins. Changes in the glycoconjungate status of the cell surface were assessed by time-course binding of the proteins during embryogenesis according to their carbohydrate-binding specificity. Glucose/mannose binding-proteins bound embryo cells at the same stage of development, at a similar stage to the N-acetylglucosamine/N-acetylneuraminic acid binding-protein (WGA) and earlier than galactose specific ones. FITC-conjugates of these proteins confirmed the above results and revealed the presence of specific and differential receptors for them. Inhibition assays using inhibitory glycoproteins significantly diminished the labelled patterns of FITC-conjugates. In conclusion, the assayed proteins exhibited embryotoxicity and their binding requirements were useful for following changes in the pattern of cell surface glycoconjugates on embryo cells of sea urchin. This property could be useful in analyzing other cell types.

A novel lectin (Morniga M) from mulberry (Morus nigra) bark recognizes oligomannosyl residues in N-glycans

Morniga M is a jacalin-related and mannose-specific lectin isolated from the bark of the mulberry (Morus nigra). In order to understand the function and application of this novel lectin, the binding property of Morniga M was studied in detail using an enzyme-linked lectinosorbent assay and lectin-glycan inhibition assay with extended glycan/ligand collection. From the results, it was found that the di-, tri-, and oligomannosyl structural units of N-glycans such as those of the bovine alpha1-acid glycoprotein (gp) and lactoferrin were the most active gps, but not the O-glycans or polysaccharides including mannan from yeast. The binding affinity of Morniga M for ligands can be ranked in decreasing order as follows: gps carrying multiple N-glycans with oligomannosyl residues >> N-glycopeptide with a single trimannosyl core > Tri-Man oligomer [Man alpha1-->6(Man alpha1-->3) Man], Penta-Man oligomer [Man alpha1-->6(Man alpha1-->3)Man alpha1-->6(Man alpha1-->3) Man] > or = Man alpha1-->2, 3 or 6 Man > Man > GlcNAc, Glc >> L-Fuc, Gal, GalNAc (inactive), demonstrating the unique specificity of this lectin that may not only assist in our understanding of cell surface carbohydrate ligand-lectin recognition, but also provide informative guidelines for the application of this structural probe in biotechnological and clinical regimens, especially in the detection and purification of N-linked glycans.

Effects of polyvalency of glycotopes and natural modifications of human blood group ABH/Lewis sugars at the Galbeta1-terminated core saccharides on the binding of domain-I of recombinant tandem-repeat-type galectin-4 from rat gastrointestinal tract (G4-N)

In our recent publication, we defined core aspects of the carbohydrate specificity of domain-I of recombinant tandem-repeat-type galectin-4 from rat gastrointestinal tract (G4-N), especially its potent interaction with the linear tetrasaccharide Galbeta1-3GlcNAcbeta1-3Galbeta1-4Glc (Ibeta1-3L). The assumed role of galectin-4 as a microvillar raft stabilizer/organizer and as a malignancy-associated factor in hepatocellular and gastrointestinal carcinomas called for further refinement of its binding specificity. Thus, the effects of polyvalency of glycotopes and natural modifications of human blood group ABH/Lewis sugars at the terminal Galbeta1-core saccharides were thoroughly examined by the enzyme-linked lectinosorbent and lectin-glycan inhibition assays. The results indicate that (a) a high-density of polyvalent Galbeta1-3/4GlcNAc (I/II), Galbeta1-3GalNAc (T) and/or GalNAcalpha1-Ser/Thr (Tn) strongly favors G4-N/glycoform binding. These glycans were up to 2.3 x 10(6), 1.4 x 10(6), 8.8 x 10(5), and 1.4 x 10(5) more active than Gal, GalNAc, monomeric I/II and T, respectively; (b) while lFuc is a poor inhibitor, its presence as alpha1-2 linked to terminal Galbeta1-containing oligosaccharides, such as H active Ibeta1-3L, markedly enhances the reactivities of these ligands; (c) when blood group A (GalNAcalpha1-) or B (Galalpha1-) determinants are attached to terminal Galbeta1-3/4GlcNAc (or Glc) oligosaccharides, the reactivities are also increased; (d) with lFucalpha1-3/4 linked to sub-terminal GlcNAc, the reactivities of these haptens are reduced; and (e) short chain Le(a)/Le(x)/Le(y) and the short chains of sialyl Le(a)/Le(x) are poor inhibitors. These distinct binding features of G4-N establish the important concept of affinity enhancement by high density polyvalencies of glycotopes (vs. multi-antennary I/II) and by introduction of an ABH key sugar to Galbeta1-terminated core glycotopes. The polyvalent ligand binding properties of G4-N may help our understanding of its crucial role for cell membrane raft stability and provide salient information for the optimal design of blocking substances such as anti-tumoral glycodendrimers.

Lectinochemical studies on the glyco-recognition factors of a Tn (GalNAcα1→Ser/Thr) specific lectin isolated from the seeds of Salvia sclarea

The lectin extracted from the seeds of Salvia sclarea (SSL) recognizes the Tn antigen (GalNAc alpha1-->Ser/Thr) expressed in certain human carcinomas. In previous studies, knowledge of the binding properties of SSL was restricted to GalNAcalpha1--> related oligosaccharides and glycopeptides. Thus, the requirements of functional groups in monosaccharide and high-density polyvalent carbohydrate structural units for SSL binding and an updated affinity profile were further evaluated by enzyme-linked lectinosorbent (ELLSA) and inhibition assays. Among the glycoproteins (gps) tested for interaction, a high density of exposed Tn-containing glycoproteins such as in the armadillo salivary Tn glycoprotein and asialo ovine salivary glycoprotein reacted best with SSL. When the gps were tested for inhibition of SSL binding, which was expressed as 50% nanogram inhibition, the high density polyvalent Tn present in macromolecules was the most potent inhibitor. Among the monosaccharide and carbohydrate structural units studied, which were expressed as nanomole inhibition, GalNAc alpha1-->3GalNAc beta1-->3Gal alpha1-->4Gal beta1-->4Glc (Fp), GalNAc alpha1-->3Gal beta1-->4Glc (A(L)), GalNAc alpha1-->3GalNAc beta1-->Me (F beta), GalNAc alpha1-->3GalNAc alpha1-->Me (F alpha) and GalNAc alpha1--> Ser/Thr (Tn) were the most active ligands, being 2.5-5.0 x 10(3) and 1.25-2.5 times more active than Gal and GalNAc, respectively. From the results, it is suggested that the combining site of SSL is a shallow groove type, recognizing the monosaccharide of GalNAc as the major binding site or Tn up to the Forssman pentasaccharide (Fp). It can be concluded that the three critical factors for SSL binding are the -NH CH(3)CO at carbon-2 in Gal, the configuration of carbon-3 in GalNAc, and the polyvalent Tn (GalNAc alpha1-->Ser/Thr) present in macromolecules. These results should assist in understanding the glyco-recognition factors involved in carbohydrate-lectin interactions in biological processes. The effect of the polyvalent F alpha, F beta and GalNAc beta1-->3Gal alpha1--> (P alpha) glycotopes on binding should be examined. However, this is hampered by the lack of availability of suitable reagents.

Lectinochemical studies on the affinity of Anguilla anguilla agglutinin for mammalian glycotopes

Anguilla anguilla agglutinin (AAA) is a fucose-specific lectin found in the serum of the fresh water eel. It is suggested to be associated with innate immunity by recognizing disease-associated cell surface glycans, and has been widely used as a reagent in hematology and glycobiology. In order to gain a better understanding of AAA for further applications, it is necessary to elucidate its binding profile with mammalian glycotopes. We, therefore, analyzed the detailed carbohydrate specificity of AAA by enzyme-linked lectinosorbent assay (ELLSA) with our extended glycan/ligand collection and lectin-glycan inhibition assay. Among the glycans tested, AAA reacted well with nearly all human blood group Ah (GalNAcalpha1-->3[LFucalpha1-->2]Gal), Bh (Galalpha1-->3[LFucalpha1-->2]Gal), H LFucalpha1-->2Gal) and Leb (Fucalpha1-->2Galbeta1-->3[Fucalpha1-->4]GlcNAc) active glycoproteins (gps), but not with blood group Lea (Galbeta1-->3[Fucalpha1-->4]GlcNAc) substances, suggesting that residues and optimal density of alpha1-2 linked LFuc to Gal at the non-reducing end of glycoprotein ligands are essential for lectin-carbohydrate interactions. Blood group precursors, Galbeta1-3GalNAc (T), GalNAcalpha1-Ser/Thr (Tn) containing glycoproteins and N-linked plasma gps, gave only negligible affinity. Among the mammalian glycotopes tested, Ah, Bh and H determinants were the best, being about 5 to 6.7 times more active than LFuc, but were weaker than p-nitrophenylalphaFuc indicating that hydrophobic environment surrounding the LFuc moiety enhance the reactivity. The hierarchy of potency of oligo- and monosaccharides can be ranked as follows: p-nitrophenyl-alphaFuc > Ah, Bh and H > LFuc > LFucalpha1-->2Galbeta1-->4Glc (2'-FL) and Galbeta1-->4[LFucalpha1-->3]Glc (3'-FL), while LNDFH I (Leb hexa-), Lea, Lex (Galbeta1-->4[Fucalpha1-->3]GlcNAc), and LDFT (gluco-analogue of Ley) were inactive. From the present observations, it can be concluded that the combining site of AAA should be a small cavity-type capable of recognizing mainly H/crypto H and of binding to specific polyvalent ABH and Leb glycotopes.

Recognition profile of Bauhinia purpurea agglutinin (BPA)

Bauhinia purpurea agglutinin (BPA) is a Galbeta1-3GalNAc (T) specific leguminous lectin that has been widely used in multifarious cytochemical and immunological studies of cells and tissues under pathological or malignant conditions. Despite these diverse applications, knowledge of its carbohydrate specificity was mainly limited to molecular or submolecular T disaccharides. Thus, the requirement of high density polyvalent or multi-antennary carbohydrate structural units for BPA binding and an updated affinity profile were further evaluated by enzyme-linked lectinosorbent (ELLSA) and inhibition assays. Among the glycoproteins (gps) tested and expressed as 50% nanogram inhibition, the high density polyvalent GalNAcalpha1-Ser/Thr (Tn) and Galbeta1-3/4GlcNAc (I/II) glycotopes present on macromolecules generated a great enhancement of binding affinity for BPA as compared to their monomers. The most potent inhibitors were a Tn-containing gp (asialo OSM) and a I/II containing gp (human blood group precursor gp), which were up to 1.7 x 10(4) and 2.3 x 10(3) times more potent than monovalent Gal and GalNAc, respectively. However, multi-antennary glycopeptides, such as tri-antennary Galbeta1-4GlcNAc, which was slightly more active than II or Gal, gave only a minor contribution. Regarding the carbohydrate structural units studied by the inhibition assay, blood group GalNAcbeta1-3/4Gal (P/S) active glycotopes were active ligands. The overall binding profile of BPA was: high density polyvalent T/Tn and II clusters >>> Tn-glycopeptides (M.W. <3.0 x 10(3))/Talpha monomer > monovalent P/S > Tn monomer and GalNAc > tri-antennary II > Gal >> Man and Glc (inactive). These findings give evidence for the binding of this lectin to dense cell surface T, Tn and I/II glycoconjugates and should facilitate future usage of this lectin in biotechnological and medical applications.

Expression of binding properties of Gal/GalNAc reactive lectins by mammalian glycotopes (an updated report)

Expression of the binding properties of Gal/GalNAc specific lectins, based on the affinity of decreasing order of mammalian glycotopes (determinants) rather than monosaccharide inhibition pattern, is probably one of the best ways to express carbohydrate specifity and should facilitate the selection of lectins as structural probes for studying mammalian glycobiology. Eleven mammalian structural units have been selected to express the binding domain of applied lectins. They are: 1. F, GalNAcalpha1 --> 3GalNAc; 2. A, GalNAcalpha1 --> 3Gal; 3. T, Galbeta1 --> 3GalNAc; 4. I, Galbeta 1 --> 3GlcNAc; 5. II, Galbeta1 --> 4GlcNAc; 6. B, Galalpha1 --> 3Gal; 7. E, Galalpha1--> 4Gal; 8. L, Galbeta1 --> 4Glc; 9. P, GalNAcbeta1 --> 3Gal; 10. S, GalNAcbeta1 --> 4Gal and 11. Tn, GalNAcalpha1 --> 4Ser (Thr) of the peptide chain. Thus, the carbohydrate specificity of Gal/GalNAc reactive lectins can be divided into classes according to their highest affinity for the above disaccharides and/or Tn residue. Examples of the binding properties of these lectins can be demonstrated by Ricimus communis agglutinin (RCA1), grouped as II specific lectin and its binding property is II > I > B > T; Ahrus precatorius agglutinin (APA), classified as T and its carbohydrate specificity is T > I/II > E > B > Tn; Artocarpus integrifolia (jacalin, AIL), as T/Tn specific and its binding reactivity is T > Tn >> I (II) and Geodia cydonium (GCL), as F/A specific, and with affinity for F > Ah [GalNAcalpha1-->43(L(Fuc)alpha1-->2)Gal] >> I > L. Due to the multiple reactivity of lectins toward mammalian glycotopes, the possible existence of different combining sites or subsites in the same molecule has to be examined, and the differential binding properties of these combining sites (if any) have to be characterized. To establish the relationship among the amino acid sequences of the combining sites of plant lectins and mammalian glycotopes should be an important direction to be addressed in lectinology.

Binding profile of Artocarpus integrifolia agglutinin (Jacalin)

Artocarpus integrifolia agglutinin (Jacalin) from the seeds of jack fruits has attracted considerable attention for its diverse biological activities and has been recognized as a Galbeta1-->3GalNAc (T) specific lectin. In previous studies, the information of its binding was limited to the inhibition results of monosaccharides and several T related disaccharides, but its interaction with other carbohydrate structural units occurring in natural glycans has not been characterized. For this reason, the binding profile of this lectin was studied by enzyme linked lectinosorbent assay (ELLSA) with our glycan/ligand collection. Among glycoproteins (gps) tested for binding, high density of multi-Galbeta1-->3GalNAcalpha1--> (mT(alpha)) and GalNAcalpha1-->Ser/Thr (mTn) containing gps reacted most avidly with Jacalin. As inhibitors expressed as nanograms yielding 50% inhibition, these mT(alpha) and mTn containing glycans were about 7.1 x 10(3), 4.0 x 10(5), and 7.8 x 10(5) times more potent than monomeric T(alpha), GalNAc, and Gal. Of the sugars tested and expressed as nanomoles for 50% inhibition, Tn containing peptides, T(alpha), and the human P blood group active disaccharide (P(alpha), GalNAcbeta1-->3Galalpha1-->) were the best and about 283 times more active than Gal. We conclude that the most potent ligands for this lectin are mTn, mT, and possibly P(alpha) glycotopes, while GalNAcbeta1-->4Galbeta1-->, GalNAcalpha1-->3Gal, GalNAcalpha1-->3GalNAc, and Galalpha1-->3Gal determinants were poor inhibitors. Thus, the overall binding profile of Jacalin can be defined in decreasing order as high density of mTn, and mT(alpha) >>> simple Tn cluster > monomeric T(alpha) > monomeric P(alpha) > monomeric Tn > monomeric T > GalNAc > Gal > Methylalpha1-->Man z.Gt; Man and Glc (inactive). Our finding should aid in the selection of this lectin for biological applications.

Rotavirus infection of MA104 cells is inhibited by Ricinus lectin and separately expressed single binding domains

Various lectins were tested for blocking rotavirus infection of MA104 cells and it was observed that galactose-specific lectins were the most inhibitory. Of these Ricinus agglutinin was able to inhibit infection (by human and animal strains) at concentrations as low as 10(-9) M. In addition, in a virus overlay protein blot assay Ricinus agglutinin competed with simian rotavirus SA11 for binding to solubilized MA104 proteins. Amino acid sequence comparisons revealed similarity between the ricin toxin B subunit (which contains two separate carbohydrate-binding motifs: single binding domains (SBD) 1 and 2) and rotavirus spike protein VP4. A filamentous phage display system was used to independently express the two binding domains and while SBD1 inhibited infection of MA104 cells by CRW8, NCDV, and to a lesser extent Wa, SBD2 blocked only CRW8 and NCDV infection. Furthermore inhibition of CRW8 infection was a direct result of phage inhibiting virus attachment to cells. When amino acid 248 within SBD2 was mutated from the ricin toxin to the Ricinus agglutinin sequence this phage clone showed reduced binding to galactose and was no longer able to inhibit virus infection. Thus, rotavirus recognizes galactose as an important component of the receptor on MA104 cells.

Carbohydrate specificity of an agglutinin isolated from the root of Trichosanthes kirilowii

The root of Trichosanthes kirilowii, which has been used as Chinese folk medicine for more than two thousand years, contains a Gal specific lectin (TKA). In order to elucidate its binding roles, the carbohydrate specificities of TKA were studied by enzyme linked lectinosorbent assay (ELLSA) and by inhibition of lectin-glycoform binding. Among glycoproteins (gp) tested, TKA reacted strongly with complex carbohydrates with Galbeta1-->4GlcNAc clusters as internal or core structures (human blood group ABH active glycoproteins from human ovarian cyst fluids, hog gastric mucin, and fetuin), porcine salivary glycoprotein and its asialo product, but it was inactive with heparin and mannan (negative control). Of the sugar inhibitors tested for inhibition of binding, Neu5Ac alpha2-->3/6Galbeta1-->4Glc was the best and about 4, 14.6 and 27.7 times more active than Galbeta1-->4GlcNAc(II), Galbeta1-->3GalNAc(T) and Gal, respectively. From these results, it is suggested that this agglutinin is specific for terminal or internal polyvalent Galbeta1-->4GlcNAcbeta1-->, terminal Neu5Ac alpha2-->3/6Galbeta1-->4Glc and cluster forms of Galbeta1-->3GalNAc alpha residues. The unusual affinity of TKA for terminal and internal Galbeta1-->glycotopes may be used to explain the possible attachment roles of this agglutinin in this folk medicine to target cells.

Defining the carbohydrate specificities of aplysia gonad lectin exhibiting a peculiar D-galacturonic acid affinity

Aplysia gonad lectin (AGL), which has been shown to stimulate mitogenesis in human peripheral lymphocytes, to suppress tumor cells, and to induce neurite outgrowth and improve cell viability in cultured Aplysia neurons, exhibits a peculiar galacturonic acid/galactose specificity. The carbohydrate binding site of this lectin was characterized by enzyme-linked lectino-sorbent assay and by inhibition of AGL-glycan interactions. Examination of the lectin binding with 34 glycans revealed that it reacted strongly with the following glycoforms: most human blood group precursor (equivalent) glycoproteins (gps), two Galalpha1-->4Gal-containing gps, and two d-galacturonic acid (GalUA)-containing polysaccharides (pectins from apple and citrus fruits), but poorly with most human blood group A and H active and sialylated gps. Among the GalUA and mammalian saccharides tested for inhibition of AGL-glycan binding, GalUA mono- to trisaccharides were the most potent ones. They were 8.5 x 10(4) times more active than Gal and about 1.5 x 10(3) more active than the human blood group P(k) active disaccharide (E, Galalpha1-->4Gal). This disaccharide was 6, 28, and 120 times more efficient than Galbeta1-->3GlcNAc(I), Galbeta1-->3GalNAc(T), and Galbeta1--> 4GlcNAc (II), respectively, and 35 and 80 times more active than melibiose (Galalpha1-->6Glc) and human blood group B active disaccharide (Galalpha1-->3Gal), respectively, showing that the decreasing order of the lectin affinity toward alpha-anomers of Gal is alpha1-->4 > alpha1-->6 > alpha1-->3. From the data provided, the carbohydrate specificity of AGL can be defined as GalUAalpha1-->4 trisaccharides to mono GalUA > branched or cluster forms of E, I, and II monomeric E, I, and II, whereas GalNAc is inactive.

Forssman pentasaccharide and polyvalent Galbeta1-->4GlcNAc as major ligands with affinity for Caragana arborescens agglutinin

The binding properties of Caragana arborescens agglutinin (CAA, pea tree agglutinin) were studied by enzyme linked lectinosorbent assay (ELLSA) and by inhibition of CAA-glycan interaction. Among glycoproteins (gps) tested, CAA reacted strongly with asialo bird nest gp, asialo rat sublingual gp, human Tamm-Horsfall Sd(a(+)) urinary gp (THGP) and asialo THGP that are rich in GalNAcalpha1-->, GalNAcbeta1--> and/or Galbeta1-->4GlcNAc residues. CAA also bound tightly with multi-valent Galbeta1-->4GlcNAc (mII) containing glycoproteins (human blood group precursor gps, asialo fetuin) and asialo ovine salivary glycoprotein (Tn, GalNAcalpha1-->Ser/Thr), but CAA reacted poorly or not at all with sialylated glycoproteins tested. Of the sugars tested for inhibition of binding, Forssman pentasaccharide (F(p), GalNAcalpha1-->3GalNAcbeta1-->3Galalpha1-->4Galbeta 1-->4Glc) was the best. It was about 2.3, 9.5 and 52.6 times more active than Galbeta1-->4GlcNAc, GalNAc and Gal, respectively, and about 1.9 times more active than tri-antennary Galbeta1-->4GlcNAc (Tri-II). These results suggest that this agglutinin is mainly specific for F(p), mII and Tn clusters. This property can be used to detect human abnormal glycotopes related to F(p) and unmasked mII/Tn clusters and to study cell growth and differentiation given the lack of toxicity of this lectin toward mouse fibroblast cells.

Lectinochemical characterization of a GalNAc and multi-Galbeta1-->4GlcNAc reactive lectin from Wistaria sinensis seeds

An agglutinin that has high affinity for GalNAcbeta1-->, was isolated from seeds of Wistaria sinensis by adsorption to immobilized mild acid-treated hog gastric mucin on Sepharose 4B matrix and elution with aqueous 0.2 M lactose. The binding property of this lectin was characterized by quantitative precipitin assay (QPA) and by inhibition of biotinylated lectin-glycan interaction. Of the 37 glycoforms tested by QPA, this agglutinin reacted best with a GalNAcbeta1-->4 containing glycoprotein (GP) [Tamm-Horsfall Sd(a+) GP]; a Galbeta1-->4GlcNAc containing GP (human blood group precursor glycoprotein from ovarian cyst fluid and asialo human alpha1-acid GP) and a GalNAcalpha1-->3GalNAc containing GP (asialo bird nest GP), but poorly or not at all with most sialic acid containing glycoproteins. Among the oligosaccharides tested, GalNAcalpha1-->3GalNAcbeta1-->3Galalpha1-->4Galbeta 1-->4Glc (Fp) was the most active ligand. It was as active as GalNAc and two to 11 times more active than Tn cluster mixtures, Galbeta1--> 3/4GlcNAc (I/II), GalNAcalpha1-->3(L-Fucalpha1-->2)Gal (Ah), Galbeta1-->4Glc (L), Galbeta1-->3GalNAc (T) and Galalpha1--> 3Galalpha-->methyl (B). Of the monosaccharides and their glycosides tested, p-nitrophenyl betaGalNAc was the best inhibitor; it was approximately 1.7 and 2.5 times more potent than its corresponding alpha anomer and GalNAc (or Fp), respectively. GalNAc was 53.3 times more active than Gal. From the present observations, it can be concluded that the Wistaria agglutinin (WSA) binds to the C-3, C-4 and C-6 positions of GalNAc and Gal residues; the N-acetyl group at C-2 enhances its binding dramatically. The combining site of WSA for GalNAc related ligands is most likely of a shallow type, able to recognize both alpha and beta anomers of GalNAc. Gal ligands must be Galbeta1-->3/4GlcNAc related, in which subterminal beta1-->3/4 GlcNAc contributes significantly to binding; hydrophobicity is important for binding of the beta anomer of Gal. The decreasing order of the affinity of WSA for mammalian structural carbohydrate units is Fp >/= multi-II > monomeric II >/= Tn, I and Ah >/= E and L > T > Gal.

Further characterization of the combining sites of Bandeiraea (Griffonia) simplicifolia lectin-I, isolectin A(4)

Bandeiraea (Griffonia) simplicifolia lectin-I, isolectin A(4)(GS I-A(4)), which is cytotoxic to the human colon cancer cell lines, is one of two lectin families derived from its seed extract. It contains only a homo-oligomer of subunit A, and is most specific for GalNAcalpha1-->. In order to elucidate the GS I-A(4)-glycoconjugate interactions in greater detail, the combining site of this lectin was further characterized by enzyme linked lectino-sorbent assay (ELLSA) and by inhibition of lectin-glycoprotein interactions. This study has demonstrated that the Tn-containing glycoproteins tested, consisting of mammalian salivary glycoproteins (armadillo, asialo-hamster sublingual, asialo-ovine, -bovine, and -porcine submandibular), are bound strongly by GS I-A(4.)Among monovalent inhibitors so far tested, p-NO2-phenylalphaGalNAc is the most potent, suggesting that hydrophobic forces are important in the interaction of this lectin. GS I-A(4)is able to accommodate the monosaccharide GalNAc at the nonreducing end of oligosaccharides. This suggests that the combining site of the lectin is a shallow cavity. Among oligosaccharides and monosaccharides tested as inhibitors of the binding of GS I-A(4), the hierarchy of potencies are: GalNAcalpha1-->3GalNAcbeta1-->3Galalpha1-->4Galbeta 1-->4Glc (Forssman pentasaccharide) > GalNAcalpha1-->3(LFucalpha1-->2)Gal (blood group A)()> GalNAc > Galalpha1-->4Gal > Galalpha1-->3Gal (blood group B-like)> Gal.

Studies on the binding of wheat germ agglutinin (Triticum vulgaris) to O-glycans

The binding profile of Triticum vulgaris (WGA, wheat germ) agglutinin to 23 O-glycans (GalNAc alpha1-->Ser/Thr containing glycoproteins, GPs) was quantitated by the precipitin assay and its specific interactions with O-glycans were confirmed by the precipitin inhibition assay. Of the 28 glycoforms tested, six complex O-glycans (hog gastric mucins, one human blood group A active and two precursor cyst GPs) reacted strongly with WGA and completely precipitated the lectin added. All of the other human blood group A active O-glycans and human blood group precursor GPs also reacted well with the lectin and precipitated over two-thirds of the agglutinin used. They reacted 4-50 times stronger than N-glycans (asialo-fetuin and asialo-human alpha1 acid GP). The binding of WGA to O-glycans was inhibited by either p-NO2-phenyl alpha,betaGlcNAc or GalNAc. From these results, it is highly possible that cluster (multivalent) effects through the high density of weak inhibitory determinants on glycans, such as GalNAc alpha1-->Ser/Thr (Tn), GalNAc at the nonreducing terminal, GlcNAc beta1--> at the non-reducing end and/or as an internal residue, play important roles in precipitation, while the GlcNAc beta1-->4GlcNAc disaccharide may play a minor role in the precipitation of mammalian glycan-WGA complexes.

Histochemical localization of glycoconjugates on microglial cells in Alzheimer's disease brain samples by using Abrus precatorius, Maackia amurensis, Momordica charantia, and Sambucus nigra lectins

Four lectins (Abrus precatorius (APA), Maackia amurensis (MAA), Momordica charantia (MCA) and Sambucus nigra (SNA)) have been used to identify glycohistochemically the microglial cells (MGC) activation in autoptic brain samples from Alzheimer's disease (AD) subjects. Three of these lectins (APA, MAA and MCA) have utilized as microglial cell markers for the first time. The identification of new markers for the study of MGC is very important to better understand the role of these type of cells in the metabolic/dismetabolic control of betaA4 in AD which still represents a vexata questio.

Differential binding of human blood group Sd(a+) and Sd(a-) Tamm-Horsfall glycoproteins with Dolichos biflorus and Vicia villosa-B4 agglutinins

The binding patterns of human blood group Sd(a+) and Sd(a-) Tamm-Horsfall glycoproteins (THGPs) with respect to four GalNAc specific agglutinins were studied by quantitative precipitin assay (QPA) and enzyme linked lectinosorbent assay (ELLSA). Of the native and asialo Sd(a+) and Sd(a-) THGP tested by QPA and ELLSA, only native and asialo Sd(a+) bound well with Dolichos biflorus (DBA) and Vicia villosa-B4 (VVA-B4), while Sd(a-) THGP reacted poorly with these two lectins. Neither Sd(a+) nor Sd(a-) THGPs reacted with two other GalNAc alpha-anomer specific lectins: Codium fragile subspecies tomentosoides and Artocarpus integrifolia. Furthermore, the binding of asialo Sd(a+)THGP-VVA-B4 and native Sd(a+)THGP-DBA through GalNAc beta--> was confirmed by inhibition assay. These results demonstrate that DBA and VVA-B4 are useful reagents to differentiate between Sd(a+) and Sd(a-) THGP.

Studies on the binding site of the galactose-specific agglutinin PA-IL from Pseudomonas aeruginosa

The binding properties of Pseudomonas aeruginosa agglutinin-I (PA-IL) with glycoproteins (gps) and polysaccharides were studied by both the biotin/avidin-mediated microtiter plate lectin-binding assay and the inhibition of agglutinin-glycan interaction with sugar ligands. Among 36 glycans tested for binding, PA-IL reacted best with two glycoproteins containing Galalpha1-->4Gal determinants and a human blood group ABO precursor equivalent gp, but this lectin reacted weakly or not at all with A and H active gps or sialylated gps. Among the mammalian disaccharides tested by the inhibition assay, the human blood group Pkactive Galalpha1-->4Gal, was the best. It was 7.4-fold less active than melibiose (Galalpha1-->6Glc). PA-IL has a preference for the alpha-anomer in decreasing order as follows: Galalpha1-->6 >Galalpha1-->4 >Galalpha1-->3. Of the monosaccharides studied, the phenylbeta derivatives of Gal were much better inhibitors than the methylbeta derivative, while only an insignificant difference was found between the Galalpha anomer of methyl- and p -NO2-phenyl derivatives. From these results, it can be concluded that the combining size of the agglutinin is as large as a disaccharide of the alpha-anomer of Gal at nonreducing end and most complementary to Galalpha1-->6Glc. As for the combining site of PA-IL toward the beta-anomer, the size is assumed to be less than that of Gal; carbon-6 in the pyranose form is essential, and hydrophobic interaction is important for binding.

Bandeiraea (Griffonia) simplicifolia lectin-I, isolectin A4, reacting with Tn (Ga1NAc alpha1 --> Ser/Thr) or galabiose (Ga1 alpha1 --> 4Ga1) containing ligands

Bandeiraea (Griffonia) simplicifolia lectin-I, isolectin A4(GS I-A4) reacting with the Tn(GalNAc alpha1 --> Ser/Thr) sequence or human blood group Pk active disaccharide (E, Gal alpha1 --> 4Gal, galabiose) was studied by quantitative precipitin (QPA) and precipitin-inhibition assays. When human blood group P1 or Tn active glycoproteins were tested by QPA, GS I-A4 reacted strongly with both the Tn active glycoproteins purified from asialo porcine, ovine and armadillo submandibular glands and a P1 active glycoprotein isolated from sheep hydatid fluid. They precipitated over 80% of the lectin nitrogen added. The asialo porcine salivary glycoprotein-GS I-A4 interaction was inhibited by both Tn containing glycopeptides and Gal alpha1 --> 4Gal indicating that GS I-A4 not only reacts with human blood group A(GalNAc alpha1 --> 3Gal) and B(Gal alpha1 --> 3Gal) active disaccharides, but also recognizes the Tn sequence and the E(Gal alpha1 --> 4-Gal) ligand. From these results, the carbohydrate specificity of GS I-A4 can be defined as A, Tn > or = B and E.

Binding properties of a blood group Le(a+) active sialoglycoprotein, purified from human ovarian cyst, with applied lectins

Studies on the structures and binding properties of the glycoproteins, purified from human ovarian cyst fluids, will aid the understanding of the carbohydrate alterations occurring during the biosynthesis of blood group antigens and neoplasm formation. These glycoproteins can also serve as important biological materials to study blood group A, B, H, Le(a), Le(b), Le(x), Le(y), T and Tn determinants, precursor type I and II sequences and cold agglutinin I and i epitopes. In this study, the binding property of a cyst glycoprotein from a human blood group Le(a+) nonsecretor individual, that contains an unusually high amount (18%) of sialic acid (HOC 350) was characterized by quantitative precipitin assay with a panel of lectins exhibiting a broad range of carbohydrate-binding specificities. Native HOC 350 reacted well only with three out of nineteen lectins tested. It precipitated about 80% of Ricinus communis (RCA1), 50% of Triticum vulgaris (WGA) and 37% of Bauhinia purpurea aba (BPA) agglutinins, respectively. However, its asialo product had dramatically enhanced reactivity and reacted well with many I/II (Gal beta1 --> 3/4GcNAc), T(Gal beta1 --> 3GalNAc) and Tn(GaNIAc alphaI --> Ser/Thr) active lectins. It bound best to Jacalin, BPA, and abrin-a and completely precipitated all the lectins added. Asialo-HOC 350 also reacted strongly with Wistaria floribunda, Abrus precatorius agglutinin, ricin and RCA1 and precipitated over 75% of the lectin nitrogen added, and moderately with Arachis hypogaea, Maclura pomifera, WGA, Vicia viosa-B4, Codium fragile tomentosoides and Ulex europaeus-II. But native HOC 350 and its asialo product reacted not at all or poorly with Dolichos biflorus, Helix pomatia, Lotus tetra-gonolobus, Ulex europaeus-I, Lens culinaris lectins and Con A. The lectin-glycoform interactions through bioactive sugars were confirmed by precipitin inhibition assay. Mapping the precipitation profiles of the interactions have led to the conclusion that HOC 350 contains a large number of receptors for I/II, T, and Tn active lectins. But in the untreated (or native) substance, most of these determinants are masked by sialic acids.

Interaction of a human blood group Sd(a-) Tamm-Horsfall glycoprotein with applied lectins

Unlike the human blood group Sd(a+) Tamm-Horsfall glycoprotein (THGP), the Sd(a-) one lacks terminal GalNAcbeta1--> residues at the nonreducing ends. The binding properties of this glycoprotein and its asialo product with lectins were characterized by quantitative precipitin (QPA) and precipitin inhibition assays. Among 20 lectins tested by QPA, both native and asialo Sd(a-) THGP reacted best with Abrus precatorius and Ricinus communis and completely precipitated the lectin added. They also precipitated well Wistaria floribunda (WFA), Glycine max (SBA), Bauhinia purpurea alba, abrin-a and ricin, all of which recognize the Galbeta1--> 4GlcNAcbeta1--> sequence, although at different strength. The lectin-glycan interactions were inhibited by Galbeta1--> 4GlcNAc and Galbeta1--> 4Glc. When the precipitability of Sd(a-) THGP was compared with that of the Sd(a+) phenotype, the native Sd(a-) THGP exhibited a 40% lesser affinity for WFA, SBA, WGA and mistletoe lectin-I (ML-I). Mapping the precipitation and inhibition profiles of the present study and the results of THGP Sd(a+), it is concluded that Sd(a-) THGP showed a strongly diminished affinity for GalNAcbeta1--> active lectins (SBA and WFA) than the Sd(a+) phenotype.

Interaction of native and asialo rat sublingual glycoproteins with lectins

The binding properties of the rat sublingual glycoprotein (RSL) and its asialo product with lectins were characterized by quantitative precipitin(QPA) and precipitin inhibition(QPIA) assays. Among twenty lectins tested for QPA, native RSL reacted well only with Artocarpus integrifolia (jacalin), but weakly or not at all with the other lectins. However, its asialo product (asialo-RSL) reacted strongly with many Gal and GalNAc specific lectins-it bound best to three of the GalNAc alpha 1-->Ser/Thr (Tn) and/or Gal beta 1-->4GlcNAc (II) active lectins [jacalin, Wistaria floribunda and Ricinus communis agglutinins] and completely precipitated each of these three lectins. Asialo-RSL also reacted well with Abrus precatorius, Glycine max, Bauhinia purpurea alba, and Maclura pomifera agglutinins, and abrin-a, but not with Arachis hypogeae and Dolichos biflorus agglutinins. The interaction between asialo-RSL and lectins were inhibited by either Gal beta 1-->4GlcNAc, p-NO2-phenyl alpha-GalNAc or both. The mapping of the precipitation and inhibition profiles leads to the conclusion that the asialo rat sublingual glycoprotein provides important ligands for II (Gal beta 1-->4GlcNAc beta 1-->) and Tn (GalNAc alpha 1-->Ser/Thr) active lectins.

Binding studies on the combining site of a GalNAc alpha 1-->-specific lectin with Thomsen-Friedenreich activity prepared from green marine algae Codium fragile subspecies tomentosoides

The combining site of a GalNAc alpha 1-->-specific lectin (CFT) with Thomsen-Friedenreich (T, Gal beta 1-->3-GalNAc alpha 1-->Ser/Thr) activity, purified from the subspecies tomentosoides of green marine algae Codium fragile was studied by quantitative precipitin and precipitin-inhibition assays. Of 27 glycoforms tested, Tn (GalNAc alpha 1-->Ser/Thr) glycoprotein from armadillo submandibular glands, and asialo porcine submandibular glycoprotein, which contains T, Tn and GalNAc alpha 1-->3Gal(A) sequences, completely precipitated the lectin added, and less than 1 microgram glycoprotein was required to precipitate 50% 4.7 micrograms lectin nitrogen. However, CFT precipitated negligibly with Pneumococcus type-XIV polysaccharide and asialo human alpha 1-acid glycoprotein, that contain exclusively the human blood-type-II precursor sequence (II, Gal beta 1-->4GlcNAc) at the nonreducing ends. Among the sugar inhibitors tested, the human blood A-active trisaccharide [Ah, GalNAc alpha 1-->3 (LFuc alpha 1-->2)Gal] was the best inhibitor; it was about twice as active as the T disaccharide. Oligosaccharides without GalNAc alpha 1--> as part of their sequences were inactive, indicating that the acetamido group at C2 of galactose is essential for binding and that GalNAc is the main contributor in the T sequence for binding. From the data provided, it is clear that the combining site of CFT requires an alpha-anomer of GalNAc and recognizes Ah, internal GalNAc alpha 1--> of T and Tn determinants of glycans, but not the blood group I/II (Gal beta 1-->3/4GlcNAc) sequences. Consequently, CFT is a useful reagent for detecting GalNAc alpha 1-->-containing glycoconjugates.

Native and/or asialo-Tamm-Horsfall glycoproteins Sd(a+) are important receptors for Triticum vulgaris (wheat germ) agglutinin and for three toxic lectins (abrin-a, ricin and mistletoe toxic lectin-I)

The binding properties of human Tamm-Horsfall Sd(a+) urinary glycoprotein (THGP) and asialo-THGP with Triticum vulgaris agglutinin(WGA) and three toxic lectins (abrin-a, ricin, and Mistletoe toxic lectin-I) were investigated by quantitative precipitin and precipitin inhibition assays. Both glycoproteins reacted strongly with abrin-a, precipitating over 80% of the lectin nitrogen tested. THGP also bound well to mistletoe toxic lectin-I and precipitated 86% of this lectin added, while the precipitability of its asialo product decreased by 28%. The native glycoprotein completely precipitated the WGA added, but its reactivity was reduced dramatically after desialylation. On the contrary, the poor reactivity of THGP with ricin increased substantially after removal of sialic acid and completely precipitated the lectin added. The glycoprotein-lectin interactions were inhibited by one or several of the following haptens, p-NO2-phenyl alpha GalNAc, p-NO2-phenyl beta GalNAc, Gal beta 1-->4GlcNAc, Gal beta 1-->4Glc, GlcNac beta 1-->4GlcNAc and/or GlcNAc. From the above results, it is concluded that native and/or Tamm-Horsfall glycoproteins serve as important receptors for these three toxic lectins and for WGA.

Fraction A of armadillo submandibular glycoprotein and its desialylated product as sialyl-Tn and Tn receptors for lectins

Fraction A of the armadillo submandibular glycoprotein (ASG-A) is one of the simplest glycoproteins among mammalian salivary mucins. The carbohydrate side chains of this mucous glycoprotein have one-third of the NeuAc alpha 2-->6GalNAc (sialyl-Tn) sequence and two thirds of Tn (GalNAc alpha-->Ser/Thr) residues. Those of the desialylated product (ASG-Tn) are almost exclusively unsubstituted GalNAc residues (Tn determinant). When the binding properties of these glycoproteins were tested by a precipitin assay with Gal, GalNAc and GlcNAc specific lectins, it was found that ASG-Tn reacted strongly with all of the Tn-active lectins and completely precipitated Vicia villosa (VVL both B4 and mixture of A and B), Maclura pomifera (MPA), and Artocarpus integrifolia (jacalin) lectins. However, it precipitated poorly or negligibly with Ricinus communis (RCA1); Dolichos biflorus (DBA); Viscum album, ML-I; Arachis hypogaea (PNA), and Triticum vulgaris (WGA). The reactivity of ASG-A (sialyl-Tn) was as active as that of ASG-Tn with MPA and less or slightly less active than that of ASG-Tn with VVL-A+B, VVL-B4, HPA, WFA, and jacalin, as one-third of its Tn was sialylated. These findings indicate that ASG-A and its desialylated product (ASG-Tn) are highly useful reagents for the differentiation of Tn, T (Gal beta 1-->3GalNAc), A (GalNAc alpha 1-->3Gal) or Gal specific lectins and monoclonal antibodies against such epitopes.

Characterization of the okra mucilage by interaction with Gal, GalNAc and GlcNAc specific lectins

A bio-active polysaccharide, which was the major component of the extract of the common okra, Hibiscus esculentus, was isolated from the extract by precipitation with ethanol between 28.5 to 45%. According to a previous report (Whistler, R.L. and Conrad, H.E. (1954) J. Am. Chem. Soc. 76, 1673-1674), this polysaccharide contains the Gal alpha 1-->4Gal sequence, which is the ligand for the uropathogenic Escherichia coli and toxic lectins. Analysis of the binding property of the okra polysaccharide by precipitin assay with Gal, GalNAc and GlcNAc specific lectins showed that this okra mucilage reacted best with Mistletoe toxic lectin-I (ML-I) and precipitated over 80% of the ML-I nitrogen (5.1 micrograms N) added. It also precipitated well with Abrus precatorius (APA), Momordica charantia (MCA) and Ricinus communis (RCA1) agglutinins, but poorly with other lectins. The results obtained suggest that this polysaccharide is a valuable reagent to differentiate Gal specific lectins from the GalNAc and/or GlcNAc specific series.

A sheep hydatid cyst glycoprotein as receptors for three toxic lectins, as well as Abrus precatorius and Ricinus communis agglutinins

The binding properties of a glycoprotein with blood group P1 specificity isolated from sheep hydatid cyst fluid with Gal and GalNAc specific lectins was investigated by quantitative precipitin and precipitin inhibition assays. The glycoprotein completely precipitated Ricinus communis agglutinin (RCA1), Abrus precatorius agglutinin (APA) and Mistletoe toxic lectin-I (ML-I). Only 1.0 microgram of P1 glycoprotein was required to precipitate 50% of 5.1 micrograms ML-I nitrogen. It also reacted well with abrin-a and ricin, precipitating over 73% of the lectin nitrogen added, but poorly or weakly with Dolichos biflorus (DBL), Vicia villosa (VVL, a mixture of A4, A2B2 and B4), VVL-B4, Arachis hypogaea (PNA), Maclura pomifera (MPL), Bauchinia purpurea alba (BPL) and Wistaria floribunda (WFL) lectins. When an inhibition assay in the range of 5.1 micrograms N to 5.9 micrograms N of lectins (ML-I, abrin-a; ricin, RCA1, and APA, and 10 micrograms P1 active glycoprotein interaction was performed; from 76 to 100% of the precipitations were inhibited by 0.44 and 0.52 mumol of Gal alpha 1-->4Gal and Gal beta 1-->4GlcNAc, respectively, but not or insignificantly with 1.72 mumol of GlcNAc. The Gal alpha 1-->4Gal disaccharide found in this P1 active glycoprotein is a frequently occurring sequence of many glycosphingolipids located at the surface of mammalian cell membranes, especially human erythrocytes and intestinal cells for ligand binding and microbial toxin attachment. The present finding suggests that the Gal alpha 1-->4Gal beta 1-->4GlcNAc sequence in this P1 active glycoprotein is one of the best glycoprotein receptors for three toxic lectins (ricin, abrin-a, and ML-I) as well as for APA, and RCA1, and the result of inhibition assay implies that these lectins are recognizing part or all of the Gal alpha 1-->4Gal beta 1-->4GlcNAc sequence in the P1 active glycoprotein.

Interaction of hamster submaxillary sialyl-Tn and Tn glycoproteins with Gal, GalNAc and GlcNAc specific lectins

Hamster submaxillary glycoprotein (HSM), one of the simplest glycoproteins among mammalian salivary mucins, is composed of approximately equivalent amounts of protein, hexosamine and sialic acid. The Thr and Ser residues in the protein core account for more than half of all of the amino acid residues, while Lys, Glu, Pro and Ala are the major components of the remaining portion of amino acids. The carbohydrate side chains of this mucous glycoprotein have mainly the NeuAc-GalNAc-(sialyl-Tn) sequence (HSM), and those of the desialylated product (HSM-Tn) are almost exclusively unsubstituted GalNAc residues (Tn determinants). The binding properties of sialyl-Tn (HSM) and asialo-HSM (HSM-Tn) glycoproteins were tested by precipitin assay with Gal, GalNAc and GlcNAc specific lectins. The HSM-Tn completely precipitated Vicia villosa (VVL both B4 and mixture of A and B), Maclura pomifera (MPL), and Artocarpus integrifolia (Jacalin) lectins; less than 2 micrograms of HSM-Tn were required for precipitating 50% of 5.0-6.3 micrograms lectin nitrogen added. HSM-Tn also reacted well with Helix pomatia lectin (HPL), Wistaria floribunda lectin (WFL) and Abrus precatorius agglutinin (APA) and precipitated in each case over 81% of the lectin nitrogen added. The reactivity of HSM-Tn with other lectins (Ricinus communis, RCA1; Dolichol biflorus, DBL; Viscum album, ML-I; Arachis hypogaea, PNA, and Triticum vulgaris, WGA) was weak or negligible. The activity of sialyl-Tn (HSM) was more restricted; HSM reacted well with Jacalin, moderately with MPL and VVL-B4, but was inactive or only weakly with the other lectins used. These findings indicate that HSM and its desialylated product (HSM-Tn) are highly useful reagents for the differentiation of Tn and T/Gal specific lectins and for anti-T, Tn and Af monoclonal antibodies.

Defining carbohydrate specificity of Ricinus communis agglutinin as Gal beta 1-->4GlcNAc (II) > Gal beta 1-->3GlcNAc (I) > Gal alpha 1-->3Gal (B) > Gal beta 1-->3GalNAc (T)

To define carbohydrate specificity of Ricinus communis agglutinin (RCA1), the combining site of RCA1 was further characterized by quantitative precipitin (QPA) and precipitin-inhibition assays (QPIA). Among the oligosaccharides tested for QPIA, Gal beta 1-->4GlcNAc (II, human blood group type II precursor sequence) was found to be 7.1 times more active than Gal beta 1-->3GalNAc (T, Thomsen-Friedenreich sequence) and about 1.7 times more active than the other three disaccharides tested--Gal beta 1-->4Man, Gal beta 1-->3DAra and Gal beta 1-->6GalNAc. Gal alpha 1-->4Gal, the receptor of the uropathogenic E. coli ligand was 3.6 times less active than the II sequence. These results indicate that the beta 1-->4 linkage of the terminal Gal to subterminal GlcNAc is important as this beta 1-->4GlcNAc sequence is at least 1.6 times more active than other types of disaccharides. Among the glycoproteins examined for QPA, native and desialized bovine submandibular glycoproteins, native and desialized human plasma alpha 1-acid glycoproteins, as well as crude hog stomach mucin and its three mild acid hydrolyzed products reacted well with the lectin. These glycoproteins precipitated over 75% of the lectin nitrogen added indicating that RCA1 has the ability to recognize Gal beta 1-->4/3GlcNAc and/or the related residues at the non-reducing ends and at positions in the interior of the chains. However, Tn (GalNAc alpha 1-->Ser/Thr sequence) rich glycoproteins such as desialized ovine submandibular glycoprotein and desialized armadillo salivary glycoprotein, in which over 90% of the carbohydrate side chains are Tn determinants with none or only a trace of I/II or T determinants, precipitated poorly with RCA1. From the present and previous results obtained, the carbohydrate specificity of RCA1 can be constructed and summarized in decreasing order by lectin determinants as follows: II (Gal beta 1-->4GlcNAc) > I (Gal beta 1-->3GlcNAc) > E (Gal alpha 1-->4Gal) and B (Gal alpha 1-->3Gal) > T (Gal beta 1-->3GalNAc), while Tn (GalNAc alpha 1-->Ser/Thr) is a poor inhibitor.